Trifluoroacetaldehyde can be stably stored as a trifluoroacetaldehyde hydrate or a trifluoroacetaldehyde hemiacetal, which can be converted to various trifluoromethyl compounds either directly or, if necessary, after dehydration or dealcoholization. Thus, the compound is highly useful an intermediate to make pharmaceutical and agrochemical products and electronic materials.
Among known processes for the synthesis of trifluoroacetaldehyde are:
(1) hydrolysis of trifluorochlorobromoethane (See, for example, Patent Document 1);
(2) fluorination of trichloroacetaldehyde in the gas phase reaction (See, for example, Patent Document 2);
(3) reduction of trifluoroacetic acid or trifluoroacetate in the liquid or solid phase (See, for example, Non-Patent Document 1 and Patent Document 3); and
(4) gas phase oxidation of trifluoroethanol (Patent Document 4).
Each process has its own drawbacks as follows. The process (1) involves the use of toxic mercury compounds. The process (2) requires complex procedures to remove incompletely fluorinated by-products with unsubstituted chlorine atoms. The process (3) as described in Non-Patent Document 1 involves the use of extremely flammable metal hydrides. The same process as described in Patent Document 3 results in an insufficient conversion, so that unreacted trifluoroacetic acid must be collected. In this instance, the products of trifluoroacetaldehyde and trifluoroacetic acid both form azeotropic mixtures with water (having bps of 106° C. and 105.5° C., respectively). Therefore, the separation process is complicated.
The process (4) is relatively simple since the process does not give inseparable by-products and since unreacted 2,2,2-trifluoroethanol can be readily separated by distillation. In Patent Document 4, trifluoroacetaldehyde is obtained at a high selectivity by subjecting 2,2,2-trifluoroethanol to gas-phase oxidation using as a catalyst a metal oxide selected from the group consisting of vanadium, chromium, molybdenum, tungsten and uranium. However, the process can achieve only a low conversion and, thus, low productivity. A process described in Patent Document 5 manages to improve the conversion by using a 0.1TiO2-0.9V2O5 catalyst along with an air-ozone mixture serving as a raw material gas, and carrying out the reaction at 390 to 420° C. Nevertheless, trifluoroacetaldehyde cannot be achieved at 100% selectivity even by the use of this catalyst. Thus, hydrogen fluoride, a highly corrosive by-product resulting from this combustion process, reduces the life of the catalyst and makes it difficult to achieve good results for an extended period of time. Although the reduced catalyst life is the most important drawback of the production of trifluoroacetaldehyde by the oxidation of 2,2,2-trifluoroethanol, the above-described Patent Document fails to provide any effective solution to the problem.    Patent Document 1 Czechoslovakia Patent No. 136870    Patent Document 2 Japanese Patent Publication No. Sho 63-15254    Patent Document 3 Japanese Patent Laid-Open Publication No. Hei    Patent Document 4 U.S. Pat. No. 3,038,936    Patent Document 5 Soviet Union Patent No. 1715799    Non-Patent Document 1 J. Am. Chem. Soc., 76, 300 (1954)